Solar cells are used to convert radiant energy into electricity. Solar cells used for these purposes operate at low cost since the energy generated by such solar cells is received from the sun. Solar cells are used for a wide variety of purposes. For example, solar cells are used to pump water, provide air conditioning and to provide electricity in homes.
Generally a plurality of solar cells are used to generate heat. The solar cells are disposed in panels, there being illustratively twenty four (24) solar cells in each panel. The solar cells in each panel are connected in series. Generally a plurality of panels are used in a system and the panels are connected in series.
Occasionally a solar cell in a particular panel will become damaged or become shadowed by an obstruction. Generally the obstruction is quite large so that several adjacent solar cells in the particular panel become shadowed simultaneously. The current carrying capacity of the particular panel becomes reduced and the output from other panels in a series relationship with the particular panel reverse biases the damaged or shadowed cells. The voltage across the damaged or shadowed cells then increases in a reverse polarity until the algebraic sum of the voltages in the reverse biased cells in the panel and the undamaged or unshadowed cells on the panel reaches a negative value of about one half of a volt (-0.5 V).
The voltage across the damaged or shadowed cells then increases in a reverse polarity until the full output voltage of all of the panels appears across the damaged or shadowed cells in the particular panel. This causes the damaged or shadowed cells to break down on a reverse basis at a relatively high breakdown voltage. The damaged or shadowed cells in the particular panel then dissipate a large amount of power, particularly as a result of the relatively high reverse breakdown voltage.
The problems discussed in the previous paragraphs have been partially resolved in the prior art. In the prior art, a diode has been connected in parallel with the solar cells in each panel. Thus, if a panel has had twenty-four (24) cells in series, a diode has been connected in parallel with the series arrangement of the twenty-four (24) solar cells. In the parallel arrangement, the cathode of the diode has been connected to the positive termination of the cells in the panel and the anode of the diode has been connected to the negative termination of the cells in the panel.
The connection of the diode to the solar cells in the panel has biased the diode against current flow while all of the cells are operative in generating energy. However, when at least one of the solar cells in the panel becomes damaged or shadowed, the diode provides a low impedance path by-passing all of the solar cells in the panel. By by-passing all of the solar cells in the panel, power being dissipated in the damaged or shadowed cells in the panel is limited to, at most, that generated by the undamaged/unshadowed cells in such panel.
The connection of a diode to the solar cells in each individual one of the panels as discussed in the last two (2) paragraphs provides an advantage in the operation of the solar cells. However, it causes all of the solar cells in a panel to be by-passed even though only one or a few of the solar cells in the panel may be damaged or shadowed. As a result, the undamaged or unshadowed cells in the panel are by-passed. This limits the ability of a system including such panel to generate electrical power. It would, accordingly, be desirable to provide a system in which only the damaged or shadowed cells in the panel, rather than all of the cells in the panel, are by-passed. To applicant's best knowledge and information, no one has provided such a system as of this time.